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• Is programming or computer science in general, all about algorithms?

  - by wakandan

  As a grad student, I find it more and more common for prestigious companies (like Google, Facebook, Microsoft,...) to put algorithm questions in their test and interviews. A few startups I applied to also asked about algorithms. I wonder if algorithms fluency is the most important thing for software developer in those companies? If the answer being yes, what are the best method or resources for one to learn & practice about algorithms effectively? I can't seem to get interested in solving seemingly too complicated problems found in most textbook or websites. Though easily understand basic algorithms (like quicksort, bubblesort,...), I find it immensely difficult to remember and reuse them later. Thanks. P/S: If you ask me what I like, it's building good softwares to solve users' problems innovatively. I suppose that does not necessarily mean the software has to be very complicated.

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• Programming ... where to start?

  - by agnesb

  For the last 4 months, I've working tirelessly on a project with my partner, who is a super programmer. He did 100% of the whole mechanism that makes our site work. My job is to take care of the cosmetic aspects of the site ... thus I should say I am good enough at CSS and html. However, since we are using Drupal to build our site, from time to time, I need his help in order to figure out how to do the customization. Sometimes, I got frustrated. I know that as a partner, I should know a little bit on how to program. However, during the crunch time when you have to deliver lightning fast (we have our site built from scratch to finish in 4 weeks ... and you are all welcome to come join the fun! It's a site for programmers!) there is no time to learn from the basics. All I can do is to pick up whatever I need at the moment. Now the site is launched, I am thinking it should be time to do some learning. So, where should I start? My partner always said I need to start with Python. What's your take on this? Thanks.

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• Schliemann's method of programming language learning

  - by DVK

  Background: 19th-century German archeologist Heinrich Schliemann was of course famous for his successful quest to find and excavate the city of Troy (an actual archeological site for the Troy of Homer's Iliad). However, he is just as famous for being an astonishing learner of languages - within the space of two years, he taught himself fluent Dutch, English, French, Spanish, Italian and Portuguese, and later went on to learn seven more, including both modern and ancient Greek. One of the methods he famously used was comparison of a known text, e.g. take a book in a language one is fluent in, take a good translation of a book in a language you wish to learn, and go over them in parallel. (various sources cited the book used by Schliemann to be the Bible, or, as the link above states, a novel). Now, for the actual question. Has anyone used (or heard of) an equivalent of Schliemann's method for learning a new programming language? E.g. instead of basing the leaning on references and tutorials, take a somewhat comprehensive set of programs known to have high-quality code in both languages implementing similar/identical algorithms and learn by comparing them? I'm curious about either personal experiences of applying such an approach, or references to something published, or existance of codebases which could be used for such an approach? What got me thinking about the idea was Project Euler and some code snippets I saw on SO, in C++, Perl and Lisp.

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• Compile time Meta-programming, with string literals.

  - by Hassan Syed

  I'm writing some code which could really do with some simple compile time metaprogramming. It is common practise to use empty-struct tags as compile time symbols. I need to decorate the tags with some run-time config elements. static variables seem the only way to go (to enable meta-programming), however static variables require global declarations. to side step this Scott Myers suggestion (from the third edition of Effective C++), about sequencing the initialization of static variables by declaring them inside a function instead of as class variables, came to mind. So I came up with the following code, my hypothesis is that it will let me have a compile-time symbols with string literals use-able at runtime. I'm not missing anything I hope. template<class Instance> class TheBestThing { public: void set_name(const char * name_in) { get_name() = std::string(name_in); } void set_fs_location(const char * fs_location_in) { get_fs_location() = std::string(fs_location_in); } std::string & get_fs_location() { static std::string fs_location; return fs_location; } std::string & get_name() { static std::string name; return name; } }; struct tag {}; int main() { TheBestThing<tag> x; x.set_name("xyz"); x.set_fs_location("/etc/lala"); ImportantObject<x> SinceSlicedBread; }

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• Dynamic Programming Recursion and a sprinkle of Memoization

  - by Auburnate

  I have this massive array of ints from 0-4 in this triangle. I am trying to learn dynamic programming with Ruby and would like some assistance in calculating the number of paths in the triangle that meet three criterion: You must start at one of the zero points in the row with 70 elements. Your path can be directly above you one row (if there is a number directly above) or one row up heading diagonal to the left. One of these options is always available The sum of the path you take to get to the zero on the first row must add up to 140. Example, start at the second zero in the bottom row. You can move directly up to the one or diagonal left to the 4. In either case, the number you arrive at must be added to the running count of all the numbers you have visited. From the 1 you can travel to a 2 (running sum = 3) directly above or to the 0 (running sum = 1) diagonal to the left. 0 41 302 2413 13024 024130 4130241 30241302 241302413 1302413024 02413024130 413024130241 3024130241302 24130241302413 130241302413024 0241302413024130 41302413024130241 302413024130241302 2413024130241302413 13024130241302413024 024130241302413024130 4130241302413024130241 30241302413024130241302 241302413024130241302413 1302413024130241302413024 02413024130241302413024130 413024130241302413024130241 3024130241302413024130241302 24130241302413024130241302413 130241302413024130241302413024 0241302413024130241302413024130 41302413024130241302413024130241 302413024130241302413024130241302 2413024130241302413024130241302413 13024130241302413024130241302413024 024130241302413024130241302413024130 4130241302413024130241302413024130241 30241302413024130241302413024130241302 241302413024130241302413024130241302413 1302413024130241302413024130241302413024 02413024130241302413024130241302413024130 413024130241302413024130241302413024130241 3024130241302413024130241302413024130241302 24130241302413024130241302413024130241302413 130241302413024130241302413024130241302413024 0241302413024130241302413024130241302413024130 41302413024130241302413024130241302413024130241 302413024130241302413024130241302413024130241302 2413024130241302413024130241302413024130241302413 13024130241302413024130241302413024130241302413024 024130241302413024130241302413024130241302413024130 4130241302413024130241302413024130241302413024130241 30241302413024130241302413024130241302413024130241302 241302413024130241302413024130241302413024130241302413 1302413024130241302413024130241302413024130241302413024 02413024130241302413024130241302413024130241302413024130 413024130241302413024130241302413024130241302413024130241 3024130241302413024130241302413024130241302413024130241302 24130241302413024130241302413024130241302413024130241302413 130241302413024130241302413024130241302413024130241302413024 0241302413024130241302413024130241302413024130241302413024130 41302413024130241302413024130241302413024130241302413024130241 302413024130241302413024130241302413024130241302413024130241302 2413024130241302413024130241302413024130241302413024130241302413 13024130241302413024130241302413024130241302413024130241302413024 024130241302413024130241302413024130241302413024130241302413024130 4130241302413024130241302413024130241302413024130241302413024130241 30241302413024130241302413024130241302413024130241302413024130241302 241302413024130241302413024130241302413024130241302413024130241302413 1302413024130241302413024130241302413024130241302413024130241302413024 02413024130241302413024130241302413024130241302413024130241302413024130

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• How to create reactive tasks for programming competitions?

  - by directx

  A reactive task is sometimes seen in the IOI programming competition. Unlike batch tasks, reactive solutions take input from another program as well as outputting it. The program typically 'query' the judge program a certain number of times, then output a final answer. An example The client program accepts lines one by one, and simply echoes it back. When it encountered a line with "done", it exists immediately. The client program in Java looks like this: import java.util.*; class Main{ public static void main (String[] args){ Scanner in = new Scanner(System.in); String s; while (!(s=in.nextLine()).equals("done")) System.out.println(s); } } The judge program gives the input and processes output from the client program. In this example, it feeds it a predefined input and checks if the client program has echoed it back correctly. A session might go like this: Judge Client ------------------ Hello Hello World World done I'm having trouble writing the judge program and having it judge the client program. I'd appreciate if someone could write a judge program for my example.

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• Advice on improving programming skills, learning capabilities?

  - by anonymous-coward1234

  Hi all, After 2,5 years of professional Java programing, I still have problems that make my job difficult and, more importantly - more times that I would like to admit - not enjoyable. I would like to ask for advice by more experienced people on ways that would help me overcome them. These are the problems I have: I do not absorb new knowledge easily. Even when I understand something, after a couple of days I easily forget even basic stuff. Other co-workers, even with the same working experience, when reading new technologies put things easily into "context", and are able to compare in "real time| similar technologies they already have used. I always try to address all the issues to whatever I am doing at one go, which results in me trying to resolve too many problems at the same time, losing completely control. I find it difficult to make my mind on a single problem that I should address first, and even when I do, and find myself throwing away code that I wrote because I started addressing the wrong issue first. As far as architecture and data modeling is concerned, I have difficulty making decisions on what objects must be created, with what hierarchy, interfaces, abstraction etc. I imagine that - to a certain degree - these things come with experience. But after 2,5 years of Java programming, I would expect myself to have come much farther that I have come, both in terms of absorption and experience. Is there a way to improve my learning speed? Any books, methods, advice is welcome.

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• Handling incremental Data Modeling Changes in Functional Programming

  - by Adam Gent

  Most of the problems I have to solve in my job as a developer have to do with data modeling. For example in a OOP Web Application world I often have to change the data properties that are in a object to meet new requirements. If I'm lucky I don't even need to programmatically add new "behavior" code (functions,methods). Instead I can declarative add validation and even UI options by annotating the property (Java). In Functional Programming it seems that adding new data properties requires lots of code changes because of pattern matching and data constructors (Haskell, ML). How do I minimize this problem? This seems to be a recognized problem as Xavier Leroy states nicely on page 24 of "Objects and Classes vs. Modules" - To summarize for those that don't have a PostScript viewer it basically says FP languages are better than OOP languages for adding new behavior over data objects but OOP languages are better for adding new data objects/properties. Are there any design pattern used in FP languages to help mitigate this problem? I have read Phillip Wadler's recommendation of using Monads to help this modularity problem but I'm not sure I understand how?

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• Which linear programming package should I use for high numbers of constraints and "warm starts"

  - by davidsd

  I have a "continuous" linear programming problem that involves maximizing a linear function over a curved convex space. In typical LP problems, the convex space is a polytope, but in this case the convex space is piecewise curved -- that is, it has faces, edges, and vertices, but the edges aren't straight and the faces aren't flat. Instead of being specified by a finite number of linear inequalities, I have a continuously infinite number. I'm currently dealing with this by approximating the surface by a polytope, which means discretizing the continuously infinite constraints into a very large finite number of constraints. I'm also in the situation where I'd like to know how the answer changes under small perturbations to the underlying problem. Thus, I'd like to be able to supply an initial condition to the solver based on a nearby solution. I believe this capability is called a "warm start." Can someone help me distinguish between the various LP packages out there? I'm not so concerned with user-friendliness as speed (for large numbers of constraints), high-precision arithmetic, and warm starts. Thanks!

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• Database Functional Programming in Clojure

  - by Ralph

  "It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." - Abraham Maslow I need to write a tool to dump a large hierarchical (SQL) database to XML. The hierarchy consists of a Person table with subsidiary Address, Phone, etc. tables. I have to dump thousands of rows, so I would like to do so incrementally and not keep the whole XML file in memory. I would like to isolate non-pure function code to a small portion of the application. I am thinking that this might be a good opportunity to explore FP and concurrency in Clojure. I can also show the benefits of immutable data and multi-core utilization to my skeptical co-workers. I'm not sure how the overall architecture of the application should be. I am thinking that I can use an impure function to retrieve the database rows and return a lazy sequence that can then be processed by a pure function that returns an XML fragment. For each Person row, I can create a Future and have several processed in parallel (the output order does not matter). As each Person is processed, the task will retrieve the appropriate rows from the Address, Phone, etc. tables and generate the nested XML. I can use a a generic function to process most of the tables, relying on database meta-data to get the column information, with special functions for the few tables that need custom processing. These functions could be listed in a map(table name -> function). Am I going about this in the right way? I can easily fall back to doing it in OO using Java, but that would be no fun. BTW, are there any good books on FP patterns or architecture? I have several good books on Clojure, Scala, and F#, but although each covers the language well, none look at the "big picture" of function programming design.

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• Are functional programming languages good for practical tasks?

  - by Clueless

  It seems to me from my experimenting with Haskell, Erlang and Scheme that functional programming languages are a fantastic way to answer scientific questions. For example, taking a small set of data and performing some extensive analysis on it to return a significant answer. It's great for working through some tough Project Euler questions or trying out the Google Code Jam in an original way. At the same time it seems that by their very nature, they are more suited to finding analytical solutions than actually performing practical tasks. I noticed this most strongly in Haskell, where everything is evaluated lazily and your whole program boils down to one giant analytical solution for some given data that you either hard-code into the program or tack on messily through Haskell's limited IO capabilities. Basically, the tasks I would call 'practical' such as Aceept a request, find and process requested data, and return it formatted as needed seem to translate much more directly into procedural languages. The most luck I have had finding a functional language that works like this is Factor, which I would liken to a reverse-polish-notation version of Python. So I am just curious whether I have missed something in these languages or I am just way off the ball in how I ask this question. Does anyone have examples of functional languages that are great at performing practical tasks or practical tasks that are best performed by functional languages?

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• Programming style question on how to code functions

  - by shawnjan

  Hey all! So, I was just coding a bit today, and I realized that I don't have much consistency when it comes to a coding style when programming functions. One of my main concerns is whether or not its proper to code it so that you check that the input of the user is valid OUTSIDE of the function, or just throw the values passed by the user into the function and check if the values are valid in there. Let me sketch an example: I have a function that lists hosts based on an environment, and I want to be able to split the environment into chunks of hosts. So an example of the usage is this: listhosts -e testenv -s 2 1 This will get all the hosts from the "testenv", split it up into two parts, and it is displaying part one. In my code, I have a function that you pass it in a list, and it returns a list of lists based on you parameters for splitting. BUT, before I pass it a list, I first verify the parameters in my MAIN during the getops process, so in the main I check to make sure there are no negatives passed by the user, I make sure the user didnt request to split into say, 4 parts, but asking to display part 5 (which would not be valid), etc. tl;dr: Would you check the validity of a users input the flow of you're MAIN class, or would you do a check in your function itself, and either return a valid response in the case of valid input, or return NULL in the case of invalid input? Obviously both methods work, I'm just interested to hear from experts as to which approach is better :) Thanks for any comments and suggestions you guys have!

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• Flowcharting functional programming languages

  - by Sadface

  Flowcharting. This ancient old practice that's been in use for over 1000 years now, being forced upon us poor students, without any usefulness (or so do I think). It might work well with imperative, sequentially running languages, but what about my beloved functional programming? Sadly, I'm forced to create a flow chart for my programm (that is written in Haskell). I imagine it being easy for something like this: main :: IO () main = do someInput <- getLine let upped = map toUpper someInput putStrLn upped Which is just 3 sequenced steps, fetching data, uppercasing it, outputting it. Things look worse this time: main :: IO () main = do someInput <- fmap toUpper getLine putStrLn someInput Or like this: main :: IO () main = interact (map toUpper) Okay, that was IO, you can handle that like an imperative language. What about pure functions? An actual example: onlyMatching :: String -> [FilePath] -> [FilePath] onlyMatching ext = filter f where f name = lower ('.' : ext) == (lower . takeExtension $ name) lower = map toLower How would you flowchart that last one?

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• Dynamic programming Approach- Knapsack Puzzle

  - by idalsin

  I'm trying to solve the Knapsack problem with the dynamical programming(DP) approach, with Python 3.x. My TA pointed us towards this code for a head start. I've tried to implement it, as below: def take_input(infile): f_open = open(infile, 'r') lines = [] for line in f_open: lines.append(line.strip()) f_open.close() return lines def create_list(jewel_lines): #turns the jewels into a list of lists jewels_list = [] for x in jewel_lines: weight = x.split()[0] value = x.split()[1] jewels_list.append((int(value), int(weight))) jewels_list = sorted(jewels_list, key = lambda x : (-x[0], x[1])) return jewels_list def dynamic_grab(items, max_weight): table = [[0 for weight in range(max_weight+1)] for j in range(len(items)+1)] for j in range(1,len(items)+1): val= items[j-1][0] wt= items[j-1][1] for weight in range(1, max_weight+1): if wt > weight: table[j][weight] = table[j-1][weight] else: table[j][weight] = max(table[j-1][weight],table[j-1][weight-wt] + val) result = [] weight = max_weight for j in range(len(items),0,-1): was_added = table[j][weight] != table[j-1][weight] if was_added: val = items[j-1][0] wt = items[j-1][1] result.append(items[j-1]) weight -= wt return result def totalvalue(comb): #total of a combo of items totwt = totval = 0 for val, wt in comb: totwt += wt totval += val return (totval, -totwt) if totwt <= max_weight else (0,0) #required setup of variables infile = "JT_test1.txt" given_input = take_input(infile) max_weight = int(given_input[0]) given_input.pop(0) jewels_list = create_list(given_input) #test lines print(jewels_list) print(greedy_grab(jewels_list, max_weight)) bagged = dynamic_grab(jewels_list, max_weight) print(totalvalue(bagged)) The sample case is below. It is in the format line[0] = bag_max, line[1:] is in form(weight, value): 575 125 3000 50 100 500 6000 25 30 I'm confused as to the logic of this code in that it returns me a tuple and I'm not sure what the output tuple represents. I've been looking at this for a while and just don't understand what the code is pointing me at. Any help would be appreciated.

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• Why can't we have a single programming Language ? [closed]

  - by Kiran

  I am no expert in Programming Languages. But whenever I change the project, I am faced with Herculean challenge of learning the new programming language which takes weeks to master if not months.. With the previous experience of programming in different languages, I believe it takes few months of continuous programming to understand the amazing features the prog.language has to offer and to exploit. It makes me wonder, why cannot we have a single programming language which boasts all the amazing features from the existing programming language and make it mandatory for all the programmers to learn it.

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• Reuse Client java Socket in a Java Server

  - by user1394983

  I'm devoloping an Java server two control an android online game. It's possible save the client socket of myserversocket.accept() in a variable in Client class? This are very util because this way, server can communicate with client when server wants and no when client contact server. My actual code are: import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.net.ServerSocket; import java.net.Socket; import java.util.ArrayList; import java.util.UUID; import sal.app.shared.Packet; public class Server { private ArrayList<GameSession> games = new ArrayList<GameSession>(); private ArrayList<Client> pendent_clients = new ArrayList<Client>(); private Packet read_packet= new Packet(); private Packet sent_packet = new Packet(); private Socket clientSocket = null; public static void main(String[] args) throws ClassNotFoundException{ ServerSocket serverSocket = null; //DataInputStream dataInputStream = null; //DataOutputStream dataOutputStream = null; ObjectOutputStream oos=null; ObjectInputStream ois=null; Server myServer = new Server(); try { serverSocket = new ServerSocket(7777); System.out.println("Listening :7777"); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } while(true){ try { myServer.clientSocket = new Socket(); myServer.clientSocket = serverSocket.accept(); myServer.read_packet = new Packet(); myServer.sent_packet = new Packet(); oos = new ObjectOutputStream(myServer.clientSocket.getOutputStream()); ois = new ObjectInputStream(myServer.clientSocket.getInputStream()); //dataInputStream = new DataInputStream(clientSocket.getInputStream()); //dataOutputStream = new DataOutputStream(clientSocket.getOutputStream()); //System.out.println("ip: " + clientSocket.getInetAddress()); //System.out.println("message: " + ois.read()); //dataOutputStream.writeUTF("Hello!"); /*while ((myServer.read_packet = (Packet) ois.readObject()) != null) { myServer.handlePacket(myServer.read_packet); break; }*/ myServer.read_packet=(Packet) ois.readObject(); myServer.handlePacket(myServer.read_packet); //oos.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } finally{ if( myServer.clientSocket!= null){ /*try { //myServer.clientSocket.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); }*/ } /*if( ois!= null){ try { ois.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } if( oos!= null){ try { oos.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } }*/ } } } public void handlePacket(Packet hp) throws IOException { if(hp.getOpCode() == 1) { registPlayer(hp); } } public void registPlayer(Packet p) throws IOException { Client registClient = new Client(this.clientSocket); this.pendent_clients.add(registClient); if(pendent_clients.size() == 2) { initAGame(); } else { ObjectOutputStream out=null; Packet to_send = new Packet(); to_send.setOpCode(4); out = new ObjectOutputStream(registClient.getClientSocket().getOutputStream()); out.writeObject(to_send); } } public void initAGame() throws IOException { Client c1 = pendent_clients.get(0); Client c2 = pendent_clients.get(1); Packet to_send = new Packet(); ObjectOutputStream out=null; GameSession incomingGame = new GameSession(c1,c2); games.add(incomingGame); to_send.setGameId(incomingGame.getGameId()); to_send.setOpCode(5); out = new ObjectOutputStream(c1.getClientSocket().getOutputStream()); out.writeObject(to_send); out = new ObjectOutputStream(c2.getClientSocket().getOutputStream()); out.writeObject(to_send); pendent_clients.clear(); } public Client getClientById(UUID given_id) { for(GameSession gs: games) { if(gs.getClient1().getClientId().equals(given_id)) { return gs.getClient1(); } else if(gs.getClient2().getClientId().equals(given_id)) { return gs.getClient2(); } } return null; } } With this code i got this erros: java.net.SocketException: Broken pipe at java.net.SocketOutputStream.socketWrite0(Native Method) at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92) at java.net.SocketOutputStream.write(SocketOutputStream.java:136) at java.io.ObjectOutputStream$BlockDataOutputStream.drain(ObjectOutputStream.java:1847) at java.io.ObjectOutputStream$BlockDataOutputStream.setBlockDataMode(ObjectOutputStream.java:1756) at java.io.ObjectOutputStream.writeNonProxyDesc(ObjectOutputStream.java:1257) at java.io.ObjectOutputStream.writeClassDesc(ObjectOutputStream.java:1211) at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1395) at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158) at java.io.ObjectOutputStream.writeFatalException(ObjectOutputStream.java:1547) at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:333) at Server.initAGame(Server.java:146) at Server.registPlayer(Server.java:120) at Server.handlePacket(Server.java:106) at Server.main(Server.java:63) This error ocurre when second client connect and server try to send an Packet to previous client 1 in function initGame() in this code: out = new ObjectOutputStream(c1.getClientSocket().getOutputStream()); out.writeObject(to_send); my android code is this: package sal.app; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.net.Socket; import java.net.UnknownHostException; import sal.app.logic.DataBaseManager; import sal.app.shared.Packet; import android.app.Activity; import android.os.Bundle; import android.view.Window; import android.view.WindowManager; public class MultiPlayerWaitActivity extends Activity{ private DataBaseManager db; public void onCreate(Bundle savedInstanceState) { super.requestWindowFeature(Window.FEATURE_NO_TITLE); super.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN); super.onCreate(savedInstanceState); setContentView(R.layout.multiwaitlayout); db=DataBaseManager.getSalDatabase(this); db.teste(); try { db.createDataBase(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } Socket socket = null; ObjectOutputStream outputStream = null; ObjectInputStream inputStream = null; //System.out.println("dadadad"); try { socket = new Socket("192.168.1.4", 7777); //Game = new MultiPlayerGame(new ServerManager("192.168.1.66"),new Session(), new Player("")); outputStream = new ObjectOutputStream(socket.getOutputStream()); inputStream = new ObjectInputStream(socket.getInputStream()); //dataOutputStream.writeUTF(textOut.getText().toString()); //textIn.setText(dataInputStream.readUTF()); Packet p = new Packet(); Packet r = new Packet(); p.setOpCode(1); outputStream.writeObject(p); /*try { r=(Packet)inputStream.readObject(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); }*/ //while(true){ //dataInputStream = new DataInputStream(clientSocket.getInputStream()); //dataOutputStream = new DataOutputStream(clientSocket.getOutputStream()); //System.out.println("ip: " + clientSocket.getInetAddress()); //System.out.println("message: " + ois.read()); //dataOutputStream.writeUTF("Hello!"); /*while ((r= (Packet) inputStream.readObject()) != null) { handPacket(r); break; }*/ r=(Packet) inputStream.readObject(); handPacket(r); //oos.close(); //} /*System.out.println(r.getOpCode()); if(r.getOpCode() == 5) { this.finish(); }*/ } catch (UnknownHostException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } /*finally{ if (socket != null){ try { socket.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } if (outputStream != null){ try { outputStream.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } if (inputStream != null){ try { inputStream.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }*/ //catch (ClassNotFoundException e) { // TODO Auto-generated catch block //e.printStackTrace(); //} catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void handPacket(Packet hp) { if(hp.getOpCode() == 5) { this.finish(); } this.finish(); } } Regards

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• how to multithread on a python server

  - by user3732790

  HELP please i have this code import socket from threading import * import time HOST = '' # Symbolic name meaning all available interfaces PORT = 8888 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print ('Socket created') s.bind((HOST, PORT)) print ('Socket bind complete') s.listen(10) print ('Socket now listening') def listen(conn): odata = "" end = 'end' while end == 'end': data = conn.recv(1024) if data != odata: odata = data print(data) if data == b'end': end = "" print("conection ended") conn.close() while True: time.sleep(1) conn, addr = s.accept() print ('Connected with ' + addr[0] + ':' + str(addr[1])) Thread.start_new_thread(listen,(conn)) and i would like it so that when ever a person comes onto the server it has its own thread. but i can't get it to work please someone help me. :_( here is the error code: Socket created Socket bind complete Socket now listening Connected with 127.0.0.1:61475 Traceback (most recent call last): File "C:\Users\Myles\Desktop\test recever - Copy.py", line 29, in <module> Thread.start_new_thread(listen,(conn)) AttributeError: type object 'Thread' has no attribute 'start_new_thread' i am on python version 3.4.0 and here is the users code: import socket #for sockets import time s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print('Socket Created') host = 'localhost' port = 8888 remote_ip = socket.gethostbyname( host ) print('Ip address of ' + host + ' is ' + remote_ip) #Connect to remote server s.connect((remote_ip , port)) print ('Socket Connected to ' + host + ' on ip ' + remote_ip) while True: message = input("> ") #Set the whole string s.send(message.encode('utf-8')) print ('Message send successfully') data = s.recv(1024) print(data) s.close

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• Book Review: Programming Windows Identity Foundation

  - by DigiMortal

  Programming Windows Identity Foundation by Vittorio Bertocci is right now the only serious book about Windows Identity Foundation available. I started using Windows Identity Foundation when I made my first experiments on Windows Azure AppFabric Access Control Service. I wanted to generalize the way how people authenticate theirselves to my systems and AppFabric ACS seemed to me like good point where to start. My first steps trying to get things work opened the door to whole new authentication world for me. As I went through different blog postings and articles to get more information I discovered that the thing I am trying to use is the one I am looking for. As best security API for .NET was found I wanted to know more about it and this is how I found Programming Windows Identity Foundation. What’s inside? Programming WIF focuses on architecture, design and implementation of WIF. I think Vittorio is very good at teaching people because you find no too complex topics from the book. You learn more and more as you read and as a good thing you will find that you can also try out your new knowledge on WIF immediately. After giving good overview about WIF author moves on and introduces how to use WIF in ASP.NET applications. You will get complete picture how WIF integrates to ASP.NET request processing pipeline and how you can control the process by yourself. There are two chapters about ASP.NET. First one is more like introduction and the second one goes deeper and deeper until you have very good idea about how to use ASP.NET and WIF together, what issues you may face and how you can configure and extend WIF. Other two chapters cover using WIF with Windows Communication Foundation (WCF) band   Windows Azure. WCF chapter expects that you know WCF very well. This is not introductory chapter for beginners, this is heavy reading if you are not familiar with WCF. The chapter about Windows Azure describes how to use WIF in cloud applications. Last chapter talks about some future developments of WIF and describer some problems and their solutions. Most interesting part of this chapter is section about Silverlight. Who should read this book? Programming WIF is targeted to developers. It does not matter if you are beginner or old bullet-proof professional – every developer should be able to be read this book with no difficulties. I don’t recommend this book to administrators and project managers because they find almost nothing that is related to their work. I strongly recommend this book to all developers who are interested in modern authentication methods on Microsoft platform. The book is written so well that I almost forgot all things around me when I was reading the book. All additional tools you need are free. There is also Azure AppFabric ACS test version available and you can try it out for free. Table of contents Foreword Acknowledgments Introduction Part I Windows Identity Foundation for Everybody 1 Claims-Based Identity 2 Core ASP.NET Programming Part II Windows Identity Foundation for Identity Developers 3 WIF Processing Pipeline in ASP.NET 4 Advanced ASP.NET Programming 5 WIF and WCF 6 WIF and Windows Azure 7 The Road Ahead Index

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• VNC error: "Could not connect to session bus: Failed to connect to socket"

  - by GJ

  I started a vncserver on display :1 on an ubuntu machine. When I connect to it, I get a grey X window with an error message Could not connect to session bus: Failed to connect to socket. The vnc log is: Xvnc Free Edition 4.1.1 - built Apr 9 2010 15:59:33 Copyright (C) 2002-2005 RealVNC Ltd. See http://www.realvnc.com for information on VNC. Underlying X server release 40300000, The XFree86 Project, Inc Sun Mar 20 15:33:59 2011 vncext: VNC extension running! vncext: Listening for VNC connections on port 5901 vncext: created VNC server for screen 0 error opening security policy file /etc/X11/xserver/SecurityPolicy Could not init font path element /usr/X11R6/lib/X11/fonts/Type1/, removing from list! Could not init font path element /usr/X11R6/lib/X11/fonts/Speedo/, removing from list! Could not init font path element /usr/X11R6/lib/X11/fonts/misc/, removing from list! Could not init font path element /usr/X11R6/lib/X11/fonts/75dpi/, removing from list! Could not init font path element /usr/X11R6/lib/X11/fonts/100dpi/, removing from list! cat: /var/run/gdm/auth-for-link2-eGnVvf/database: No such file or directory gnome-session[24880]: WARNING: Could not make bus activated clients aware of DISPLAY=:1.0 environment variable: Failed to connect to socket /tmp/dbus-FhdHHIq8jt: Connection refused gnome-session[24880]: WARNING: Could not make bus activated clients aware of GNOME_DESKTOP_SESSION_ID=this-is-deprecated environment variable: Failed to connect to socket /tmp/dbus-FhdHHIq8jt: Connection refused gnome-session[24880]: WARNING: Could not make bus activated clients aware of SESSION_MANAGER=local/dell:@/tmp/.ICE-unix/24880,unix/dell:/tmp/.ICE-unix/24880 environment variable: Failed to connect to socket /tmp/dbus-FhdHHIq8jt: Connection refused Sun Mar 20 15:34:10 2011 Connections: accepted: 0.0.0.0::51620 SConnection: Client needs protocol version 3.8 SConnection: Client requests security type VncAuth(2) VNCSConnST: Server default pixel format depth 16 (16bpp) little-endian rgb565 VNCSConnST: Client pixel format depth 16 (16bpp) little-endian rgb565 gnome-session[24880]: Gtk-CRITICAL: gtk_main_quit: assertion `main_loops != NULL' failed gnome-session[24880]: CRITICAL: dbus_g_proxy_new_for_name: assertion `connection != NULL' failed Any ideas how to fix it?

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• exiting from a blocking select call!

  - by Jay

  I am calling a third party API which creates a socket, does a connect and then calls select API by passing the socket to block forever. I don't have access to the socket. Is there some way in which I can make the select call come out from my application without having access to the socket? My platform is Windows.

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• From a Java programming perspective, what difference does multicast make to a networking program?

  - by pnut butter

  My manager has asked me to assess what changes would be required to add multicast support to a socket-based TCP/IP networking program that is part of a trading system. As far as I can tell, from the perspective of a Java program, it doesn't seem to matter too much whether the program is unicast or multicast. Doesn't the Java networking API make all of this transparent? By this I mean, wouldn't the change be a simple one of simply adding additional destinations for the outgoing connections?

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• Android Activity access Unity Classes

  - by Anomaly

  I have made my own C# classes in Unity, is there any way I can access these classes from the Android Activity that starts the UnityPlayer? Example: I have a C# class called testClass in Unity: class testClass{ public static string myString="test string"; } From the Android activity in Java I want to access that class: string str=testClass.myString; Is this possible? If so, how? Or is there some other way to do this? In the end I basically want to communicate between my Android activity and the UnityPlayer object. Thanks in advance. EDIT: Ok so I looked at building Android plugins for Unity but this wasn't satisfactory to me. I ended up building a socket client-server interface in Unity with C# and another one in Java for the Android app: So Unity listens on port X and broadcasts on port Y The Android activity listens on port Y and broadcasts on port X This is necessary as both interfaces are running on the same host. So that's how I solved my problem, but I'm open for any suggestions if anyone knows a better way of communicating between the Unityplayer and your app.

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• Embedded Prolog Interpreter/Compiler for Java

  - by Sami

  I'm working on an application in Java, that needs to do some complex logic rule deductions as part of its functionality. I'd like to code my logic deductions in Prolog or some other logic/constraint programming language, instead of Java, as I believe the resulting code will be significantly simpler and more maintainable. I Googled for embedded Java implementations on Prolog, and found number of them, each with very little documentation. My (modest) selection criteria are: should be embeddable in Java (e.g. can be bundled up with my java package instead of requiring any native installations on external programs) simple interface to use from Java (for initiating deductions, inspecting results, and adding rules) come with at least a few examples on how to use it doesn't necessarely have to be Prolog, but other logic/constraint programming languages with the above criteria would suit my needs, too. What choices do I have and what are their advantages and disadvantages?

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• Which useful alternative control structures do you know?

  - by bigown

  Similar question was closed on SO. Sometimes when we're programming, we find that some particular control structure would be very useful to us, but is not directly available in our programming language. What alternative control structures do you think are a useful way of organizing computation? The goal here is to get new ways of thinking about structuring code, in order to improve chunking and reasoning. You can create a wishful syntax/semantic not available now or cite a less known control structure on an existent programming language. Answers should give ideas for a new programming language or enhancing an actual language. Think of this as brainstorming, so post something you think is a crazy idea but it can be viable in some scenario. It's about imperative programming.

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• Why do socket.makefile objects fail after the first read for UDP sockets?

  - by Eli Courtwright

  I'm using the socket.makefile method to create a file-like object on a UDP socket for the purposes of reading. When I receive a UDP packet, I can read the entire contents of the packet all at once by using the read method, but if I try to split it up into multiple reads, my program hangs. Here's a program which demonstrates this problem: import socket from sys import argv SERVER_ADDR = ("localhost", 12345) sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) sock.bind(SERVER_ADDR) f = sock.makefile("rb") sock.sendto("HelloWorld", SERVER_ADDR) if "--all" in argv: print f.read(10) else: print f.read(5) print f.read(5) If I run the above program with the --all option, then it works perfectly and prints HelloWorld. If I run it without that option, it prints Hello and then hangs on the second read. I do not have this problem with socket.makefile objects when using TCP sockets. Why is this happening and what can I do to stop it?

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